Abstract
An oblique shock wave is generated in a Mach 2 flow at a flow deflection angle of$12^{\circ }$. The resulting shock-wave–boundary-layer interaction (SWBLI) at the tunnel wall is observed. A novel traversable shock generator allows the position of the SWBLI to be varied relative to a downstream expansion fan. The relationship between the SWBLI, the expansion fan and the wind tunnel arrangement is studied. Schlieren photography, surface oil flow visualisation, particle image velocimetry and high-spatial-resolution wall pressure measurements are used to investigate the flow. It is observed that stream-normal movement of the shock generator downwards (towards the floor and hence the point of shock reflection) is accompanied by (1) growth in the streamwise extent of the shock-induced boundary layer separation, (2) upstream movement of the shock-induced separation point while the reattachment point remains nearly fixed, (3) an increase in separation shock strength and (4) transition between regular and irregular (Mach) reflection without an increase in incident shock strength. The role of free interaction theory in defining the separation shock angle is considered and shown to be consistent with the present measurements over a short streamwise extent. An SWBLI representation is proposed and reasoned which explains the apparent increase in separation shock strength that occurs without an increase in incident shock strength.
Highlights
Shock-wave–boundary-layer interactions (SWBLIs) are encountered in many internal and external compressible flows, and can be found across a wide range of applications from gas dynamic lasers to aircraft
We present the results from experiments with a novel set-up that allows us to (1) experimentally observe transition of an incident–reflected shock-wave–boundary-layer interaction (SWBLI), (2) explore the relationship between the proximity of the downstream expansion fan and the SWBLI, and (3) investigate the applicability of free interaction theory in defining the mean separation shock angle
Several features can be seen: the shock generator, the incident shock, the reflected shock, an expansion fan, the SWBLIs themselves and a few Mach waves originating from wall joints or imperfectly cancelled waves from the nozzle expansion which are so weak that they do not influence the flow
Summary
Shock-wave–boundary-layer interactions (SWBLIs) are encountered in many internal and external compressible flows, and can be found across a wide range of applications from gas dynamic lasers to aircraft. Where they occur, SWBLIs impose a strong adverse pressure gradient on the boundary layer. SWBLIs impose a strong adverse pressure gradient on the boundary layer This adverse pressure gradient can lead to flow unsteadiness, distortion and separation. Flow separation can have a large and direct impact on the operability of a given application.
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